1. PS2561L2-1-V-A Substitution Conclusion The substitution is generally viable, though attention must be paid to the difference in Current Transfer Ratio (CTR) range. The PS2561L2-1-V-A is identical to the original part in key parameters such as isolation voltage, output current, package, and switching speed. Its maximum forward current (80 mA) is even superior to the original's (40 mA), offering greater design margin. The primary discrepancy lies in its CTR range, which is specified as 80%-400% compared to the original's 100%-200%. This results in a lower minimum and a higher maximum CTR. Consequently, for the same input current, the minimum possible output current is lower, which could potentially lead to insufficient drive capability under certain marginal conditions. Conversely, the maximum possible output current is higher, which may cause deeper saturation and a slight variation in switching speed. Provided the target circuit can accommodate this wider CTR range, particularly the lower minimum, this part can serve as a direct replacement and offers improved robustness on the drive side.